Anti-roll leaf spring suspension

ABSTRACT

Vehicle suspension comprising a pair of leaf springs ( 1 ) located or locatable on respective opposed side of a vehicle chassis ( 3 ) and extending longitudinally thereof, and an anti-roll device ( 12 ) which is arranged to extend transversely of the vehicle chassis ( 3 ), and means ( 41, 42, 46 ) mounting opposed ends ( 22, 23 ) of the anti roll device ( 12 ) rigidly to respective ones of the pair of opposed leaf springs ( 1 ).

This application is a continuation-in-part of application Ser. No.10/552,420, which is the National Stage of International Application No.PCT/GB04/00148, filed Jan. 19, 2004.

FIELD OF THE INVENTION

This invention relates to an anti-roll leaf spring suspension of thetype comprising a pair of leaf springs, with single or multiple leaves,which extend longitudinally of a vehicle chassis on opposed sidesthereof and which are connected to respective ends of anti-roll means,such as an anti-roll bar or tube, extending transversely of the vehiclechassis.

BACKGROUND OF THE INVENTION

When a vehicle travels over a road surface, the major mass of thevehicle is isolated, by its suspension, from vibrations caused byirregularities of that surface. The loads to which the vehiclesuspension is subjected, are borne by the leaf springs of the vehiclesuspension.

The softer the vehicle leaf springs, and/or the lower their loaddeflection rates are, the better the isolation.

The quality of this isolation affects the ride quality of the vehicleand any damage inflicted on the road surface thereby.

There is, however, a limitation on the degree to which the leaf springscan be softened, because the suspensions also have to control thedynamic forces exerted upon them by the mass of the vehicle duringchanges of direction and/or velocity thereof.

One such direction change occurs when a vehicle changes its direction oftravel when being driven around, say, a curve or bend in the road.

During this manoeuvre, the vehicle suspension has to accommodate thecentrifugal forces which cause the mass of the vehicle to transfer on tothe wheels on the outside of the curve or bend and from the wheels onthe inside of the curve or bend.

This mass transfer on to the outside wheels of the vehicle istransmitted to the suspension. The softer the suspension, the more theleaf springs will deflect, thus causing the vehicle to lean or roll.

Owing to the practicalities associated with the design and installationof such a suspension, as well as other dynamic vehicle handlingcharacteristics, there is a limit to the amount and rate of roll whichis acceptable. Such a limitation creates a compromise between the rideand handling qualities of the vehicle.

With such a compromise, the amount and rate of roll which is acceptable,limits the softness of the suspension and the associated quality of ridewhich is available.

To improve or resolve this compromise, additional springs or springmodifications, have been available, which resist vehicle roll, withoutincreasing the vertical spring stiffness, when both vehicle wheelsdeflect together.

Such mechanisms are usually known as “anti-roll mechanisms”.

However, as the vehicle ride is also dependent upon the vibrations towhich the suspension is subjected when only one wheel of the vehicledeflects, there is often a limit as to how much the ride and handlingcompromise can be extended.

For many years, anti-roll mechanisms have been based upon a separatetorsion bar or tube acting transversely of the vehicle between theopposed wheels of the suspension.

A recent development for vehicles which are suspended by leaf springs oneach side thereof, have been mechanisms which stiffen the springsinternally, only when the springs deflect in opposite directions, asthey do when the vehicle rolls.

Leaf springs to which a vehicle chassis is mounted, are effectivelypin-jointed beams and set as such. Usually, the leaf springs arefastened to the axle of the wheels in the region of their centres andare mounted to the vehicle chassis via bushes and/or shackles at theirrespective opposed ends.

The loads applied to the leaf springs create bending moments therein,which, in turn, cause the springs to deflect and, thus, absorb energy.

During vehicle roll, the effective mass of the vehicle is transferred,at the axle, from one spring to the other, changing the bending momentstherein. The stiffness of the leaf springs controls the change indeflection of each spring and these now different deflections in eachspring, on each side of the vehicle, create, in turn, the amount of rollin the vehicle.

In previous developments of these anti-roll techniques, a torsionallyrigid member has been connected between the leaf springs at or adjacentone end of the springs. This member, such as an anti-roll bar or tube,allows the leaf springs to work normally when they deflect together inthe same direction, as they normally function when creating thevehicle's primary ride characteristics.

As discussed above, when the vehicle rolls, the leaf springs deflect indifferent directions as the vehicle mass is transferred to the outsidespring from the inside spring. During such deflections, the torsionallyrigid member resists the angular differences between the two opposedleaf springs, thereby creating a deflection resisting moment in thesprings, which then produces a lower change in bending moment in thesprings. This, in effect, changes the pin-jointed beam nature of thesprings into fixed-ended, or encastre, beams.

This lower-than-previous change in bending moment creates smaller springdeflections and thus stiffens the springs during roll only.

Therefore, adding the torsionally stiff member to the ends of the leafsprings, creates an effective anti-roll mechanism.

In practice, this additional bending moment is applied over the physicallength of the brackets mounting the torsionally rigid member to the endsof the opposed leaf springs.

Also, it can be seen that this anti-roll mechanism reduces the maximum,and any change in the, bending moment and, therefore, increases theservice life of the leaf springs.

In practice also, this mechanism is more effective as an anti-rollmechanism than suggested above. If the torsionally rigid member is addedto just one end of the pair of opposed leaf springs, the resultantanti-roll mechanism stiffens just one end of the leaf springs when thevehicle rolls. This creates asymmetrical cantilever deflecting leafsprings, which means that, during vehicle roll, the axle seat area ofeach leaf spring, which is fastened centrally to the axle, attempts todeflect in different angular directions. Such deflection is resisted bythe torsional rigidity of the axle which, again, tends to stiffen-up theleaf springs. This anti-roll stiffness associated with asymmetricalsprings is well known in spring and suspension design practice.

Whilst this anti-roll stiffening of the leaf springs can be veryeffective, some applications can benefit from even higher and extraspring stiffening for resisting vehicle roll. This could allow thenormal ride stiffness to be lowered even further, thus improving thebasic vehicle ride and creating an even better compromise between ridequality and anti-roll vehicle handling stability.

To summarise current prior art anti-roll suspension designs, it isnormal practise to mount the torsionally rigid member as close aspossible to the neutral axis in bending of the leaf springs.

Also, the mountings between the torsionally rigid member and the opposedleaf springs are made sufficiently flexible to allow for thetransmission of torque created by the member but to be consideredpin-jointed in plan view.

This is achieved by making the brackets mounting the opposed ends of thetorsionally rigid member to the ends of the leaf springs, sufficientlynarrow or otherwise flexible, to allow the member to move within thosemountings.

This is considered to be normal practice to improve assembly, reducelocal stresses, create a lightweight structure and avoid interferingwith the normal spring deflections.

It is an object of the present invention to provide a leaf springsuspension which provides, during roll of the associated vehicle,further stiffening of the springs beyond that achieved to date, asdiscussed above, to improve the anti-roll characteristic of thesuspension and, as a consequence, its performance and durability.

SUMMARY OF THE INVENTION

Accordingly, the invention provides a suspension for a vehicle,comprising a pair of leaf springs located or locatable on respectiveopposed sides of a vehicle chassis and extending longitudinally thereof,and an anti-roll device which is arranged to extend transversely of thevehicle chassis, and means mounting opposed ends of the anti-roll devicerigidly to respective ones of the pair of opposed leaf springs.

Preferably, the mounting means is arranged to clamp the opposed ends ofthe anti-roll device rigidly to respective ones of the pair of opposedleaf springs.

This rigid clamping or other form of mounting effectively renders themounted end of the anti-roll device fixed or so-called “encastre” inbending, when viewed in plan, thereby exploiting the anti-roll device'sbending stiffness to create higher anti-roll stiffening of the leafsprings.

The anti-roll device may have its opposed ends mounted rigidly by themounting means to any position along the lengths of the pair of opposedleaf springs, although at least one end of those leaf springs ispreferred.

The rigidity of the mounting of the anti-roll device to the leafsprings, as provided by the clamping or other mounting means, creates ahigher resistance force to bending of the anti-roll device, in planview, which occurs when the leaf springs deflect in opposite directionsduring, say, vehicle roll. This higher-than-previous resistance forcecreates a bending moment in the leaf springs when it acts offset fromthe neutral axis in bending of the springs, which resists the change inbending reducing, in turn, leaf spring deflection during vehicle roll.Thus, the extra bending rigidity stiffens the springs during vehicleroll and creates this extra anti-roll resistance within the suspension.

The opposed ends of the anti-roll device may be offset from the neutralplane in bending of each of the opposed leaf springs by means ofspacers.

In a preferred embodiment to be described hereinbelow, the mountingmeans provides a comparatively large clamping area, which has previouslybeen comparatively small, between the mounting means and the anti-rolldevice.

The anti-roll device itself may be of any suitable form, for instance, abeam, bar or tube.

According to another aspect of the invention, there is provided a methodof increasing spring stiffness during vehicle roll, in which leafsprings extending longitudinally of a vehicle chassis on opposed sidesthereof deflect in different directions, the method comprising mountingopposed ends of an anti-roll device that extends transversely to thevehicle chassis to respective ones of the leaf springs so rigidly as toprevent any and all relative movement of the opposed ends of theanti-roll device to the respective ones of the leaf spring to make theanti-roll device into a fixed ended characteristic beam in plan viewsuch that when the springs deflect in different directions to eachother, as in vehicle roll, the springs change from pin-jointed beamstowards fixed ended characteristic beams, thus substantially increasingthe stiffness of the springs.

According to yet another aspect of the invention, there is provided amethod of increasing spring stiffness during vehicle roll, in which leafsprings that extend longitudinally of a chassis of a vehicle on opposedsides thereof deflect in different directions, the method comprising:

(a) mounting opposed ends of an anti-roll device that extendstransversely to the vehicle chassis to respective ones of the leafsprings so rigidly as to prevent any and all relative movement of theopposed ends of the anti-roll device to the respective ones of the leafspring to make the anti-roll device into a fixed ended characteristicbeam in plan view; and

(b) when the springs deflect in different directions to each other, asin vehicle roll, changing the springs from pin-jointed beams towardsfixed ended characteristic beams, thus substantially increasing thestiffness of the springs.

Preferably these methods include mounting the opposed ends of theanti-roll device at a substantial offset distance from a neutral axis inbending of the springs such that when the springs deflect in oppositedirections, as in vehicle roll, resistant forces combine with the offsetdistance from the neutral axis to create moments in the springs tofurther change spring bending characteristics from pin-jointed to fixedended beam characteristics, thus further substantially increasing thestiffness of the springs.

According to an additional aspect of the invention, there is provided amethod of increasing spring stiffness during vehicle roll, in which leafsprings extending longitudinally of a vehicle chassis on opposed sidesthereof deflect in different directions, in use of a vehicle havingopposed ends of an anti-roll device that extends transversely to thevehicle chassis mounted to respective ones of the leaf springs at asubstantial offset distance from a neutral axis in bending of thesprings so rigidly as to prevent any and all relative movement of theopposed ends of the anti-roll device to the respective ones of the leafspring to make the anti-roll device into a fixed ended characteristicbeam in plan view, the method comprising, when the springs deflect indifferent directions to each other, as in vehicle roll, (i) changing thesprings from pin-jointed beams towards fixed ended characteristic beams,thus substantially increasing the stiffness of the springs, and (ii)combining resistant forces with the offset distance from the neutralaxis to create moments in the springs to further change spring bendingcharacteristics from pin-jointed to fixed ended beam characteristics,thus further substantially increasing the stiffness of the springs.

The arrangement at each end of the anti-roll device rigidly mounting theanti-roll device to the respective spring may feature U-bolts embracingaround the spring and fastened to a clamping piece lying against theanti-roll device to clamp the anti-roll device and spring together withsufficient fastening tightness to retain an absolute rigidity of thisclamping during in typical use conditions of the suspension. An opposingclamping piece is preferably disposed between each U-bolt and therespective spring where a closed end of the U-bolt extends about thespring.

Alternatively, straight bolts fastened tightly to the clamping piece mayengage a larger opposing clamping piece on the side of the springopposite the anti-roll device to clamp the anti-roll device and springtogether between the clamping pieces, the larger clamping pieceextending outwardly past opposite sides of the spring to receive passageof the bolts through it.

In a further alternative mounting arrangement at each end of theanti-roll device, support plates welded to the anti-roll device mayproject in a common direction from therefrom at spaced apart positionstherealong to lie on opposite sides of the spring, clamping pieces beingfastened to the support members to therebetween with the spring passingthrough the space between the clamping pieces and being held in placetherebetween. A bolt may be passed through the spring and clampingpieces and be tightly fastened to ensure rigidity of the spring'sclamping between the clamping pieces.

Each spring is preferably a single-leaf spring.

Alternatively, a multi-leaf spring may be used with low frictioninterleaves disposed between leaves of the spring and between theanti-roll device and a leaf of the spring nearest thereto to allowsliding shearing movement between the leaves under deflection of thespring, the interleaves being highly compressed between the leaves toprevent any further compression under exposure to further compressionloads in use of the springs and thereby prevent any space from openingin a stack of the leaves and interleaves between the anti-roll deviceand a clamping piece across the spring from the anti-roll device to keepthe anti-roll device rigidly clamped to the spring at a fixed positionalong a furthest leaf from the anti-roll device in the stack.

Cooperating matable elements at the interface of the furthest leaf andthe clamping piece may positively locate the mounting arrangement at thefixed position along the furthest leaf. The cooperating elements may bea dowel pin and respective blind holes in the two members, a stud on onemember and hole in the other, or a bump on one member and dimple in theother.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more fully understood, embodiments ofsuspension in accordance therewith will now be described by way ofexample and comparison with existing prior art suspensions, withreference to the accompanying drawings in which:

FIG. 1 is a perspective, generally diagrammatic view of a prior art leafspring suspension without an associated anti-roll device;

FIG. 2 is a diagrammatic side elevation of the springs of the suspensionshown in FIG. 1;

FIG. 3 is a simplistic bending moment diagram for the springs of thesuspension shown in FIGS. 1 and 2;

FIG. 4 is a simplistic bending moment diagram for the suspension springsshown in FIGS. 1 and 2, under vehicle roll conditions;

FIG. 5 is a perspective diagrammatic view of a prior art suspensionfitted with an anti-roll device;

FIG. 6 is a simplistic bending moment diagram for the springs of thesuspension shown in FIG. 5 under vehicle roll conditions;

FIG. 7 is a diagrammatic side view of a suspension in accordance withthe invention, in its steady state condition;

FIG. 8 is a side view of the suspension shown in FIG. 7, with its leafsprings in respective rebound and compression configuration;

FIG. 9 is a plan view of the leaf spring suspension shown in FIG. 8,with the springs in their respective rebound and compressionconfigurations;

FIG. 10 is a simplistic bending moment diagram for the first embodimentof leaf spring suspension shown in FIGS. 7 to 9; and

FIGS. 11 to 13 are respective plan, end and side views of a firstembodiment detail of the leaf spring suspension shown in FIGS. 7 to 9,showing a first embodiment form of mounting means therefor.

FIGS. 14 to 16 are respective plan, end and side view of a secondembodiment detail of the leaf spring suspension shown in FIGS. 7 to 9,showing a second embodiment form of the mounting means therefore.

FIGS. 17 to 19 are respective plan, end and side view of a thirdembodiment detail of the leaf spring suspension shown in FIGS. 7 to 9,showing a third embodiment form of the mounting means therefore.

FIGS. 20 and 21 are respective plan, end and side view of a fourthembodiment detail of the leaf spring suspension shown in FIGS. 7 to 9,showing a fourth embodiment form of the mounting means therefore.

DETAILED DESCRIPTION

For a better understanding of the improved anti-roll capabilities of asuspension in accordance with the invention, two known prior art leafspring suspensions will be discussed initially.

As indicated above, leaf springs on vehicles act effectively aspin-jointed beams and are usually mounted to the vehicle axle at oradjacent their centres and to the vehicle chassis via bushes and/orshackles at their respective opposed ends.

Such a prior art suspension is shown in FIG. 1, wherein a pair ofgenerally parallel leaf springs 1 are mounted, at their centres, torespective opposed end regions of an axle 2.

The leaf springs 1 extend longitudinally of the chassis 3 of theassociated vehicle (not shown) and the axle has a pair of running wheels4 at respective opposed ends thereof.

The fore and aft ends of each leaf spring 1 are mounted to the vehiclechassis 3 by respective brackets 5,6 and associated bushes 7 andshackles 8 in known manner.

Effectively, the fore and aft ends of each leaf spring 1 are pin-jointedat 9 and the lower bush 10 of the shackle 8, the upper bush 10 of eachshackle 8 being shown in FIG. 1, so that the fore and aft cantileversections of each leaf spring 1 in effect act as pin-jointed beams.

The loads L applied to the leaf springs 1, as shown in FIG. 2, create abending moment in each leaf spring 1, as shown in the bending momentdiagram 11 of FIG. 3.

Such bending moment causes each leaf spring 1 to deflect, therebyabsorbing energy during normal working of the suspension when the leafsprings 1 deflect together.

During vehicle roll, however, the mass of the vehicle is transferred, atthe axle 2, from one spring 1 to the other, creating bending moments, asshown by the respective bending moment diagrams 12,13 of FIG. 4.

The stiffness of the leaf springs 1 controls the change in deflection ofeach spring 1 and these now different deflections in the springs 1, oneach side of the associated vehicle, create, in turn, the amount of rollto which the vehicle is subjected.

Thus, in FIG. 4, as in FIG. 3, the steady state, bending moment diagramis represented at 11, whilst the unrestricted compression, bendingmoment diagram for the leaf spring 1 on the outside of a curve or bendbeing negotiated by the vehicle, is indicated at 12.

The unrestricted rebound, bending moment diagram for the leaf spring onthe inside of the bend or curve being negotiated by the vehicle, isshown at 13.

In the development of prior art, anti-roll systems, a torsionally rigidmember, such as an anti-roll bar or tube, is mounted transversely of thevehicle chassis 3, with its opposed ends mounted at or adjacent the foreand aft ends of the leaf springs 1.

Such an anti-roll suspension arrangement is shown in FIG. 5, with thetorsionally rigid member indicated at 12.

This member 12, usually in the form of a beam, bar of tube, permits theleaf springs 1 of the suspension to work normally when they deflecttogether in the same direction, as they function normally when creatingthe vehicle's primary ride characteristics.

When, however, the vehicle rolls, for example, when negotiating a bendor curve, the leaf springs 1 deflect in different directions, as themass of the vehicle is transferred to the outside leaf spring.

During these deflections, the torsionally rigid member 12 resists theangular differences between the two leaf springs 1, creating adeflection resisting moment in the springs 1, which then produces alower change in bending moment in the springs 1.

This, in effect, changes the pin-jointed beams, represented by the leafsprings 1, into fixed-end, or encastre, beams.

This change in bending moments is illustrated in FIG. 6 in which thesteady state bending moment diagram is again shown at 11, theunrestricted compression bending moment diagram, at 12 and theunrestricted rebound bending moment diagram, at 13.

The revised compression bending moment diagram resulting from theresisting moment b provided by the torsionally rigid member 12 of thesuspension, shown in FIG. 5 is represented at 14, whilst the revisedrebound bending moment diagram, again resulting from the resistingmoment b provided by the torsionally rigid member 12, is shown at 15.

These lower changes in bending moments, as represented by the bendingmoment diagrams 14 and 15 in FIG. 6, create smaller-than-previous springdeflections and, thus, stiffen the leaf springs 1 during roll only.

Thus, adding the torsionally stiff member 12 to the leaf springs 1 ofthe suspension, creates an effective anti-roll mechanism.

For simplicity, the bending moment diagrams of FIG. 6 show the addeddeflection resisting moment, as if it were applied directly to the endsof the leaf springs 1. In practice, this additional moment would beapplied over the physical length of the means, such as brackets, used tomount the torsionally rigid member 12 to the springs 1.

Also, it can be seen that the anti-roll device reduces the maximum, aswell as change, in bending moment and, therefore, increases the servicelife of the springs 1.

In practice, this device is more effective as an anti-roll mechanismthan suggested above.

If the torsionally rigid member 12 is mounted to just one cantilever,for example, the fore cantilever, of each leaf spring 1, as shown inFIG. 5, the effective anti-roll mechanism stiffens only one cantilever,or end, of each spring 1 when the associated vehicle undergoes roll.This creates asymmetrical cantilever deflecting springs which means thatduring vehicle roll, the seat area of the axle 2, which is mountedcentrally of each leaf spring 1, attempts to deflect in differentangular directions, this being resisted by the inherent torsionalrigidity of the axle 2, again stiffening the springs 1.

This anti-roll stiffness of asymmetrical leaf springs is well known inspring and suspension design practice.

Whilst this prior art anti-roll mechanism can be effective, someapplications can benefit from even higher, extra spring stiffening toresist vehicle roll. Such would allow the normal ride stiffness to belowered even further, thus improving the basic ride when the springs 1move together in the same direction. Such additional stiffness wouldcreate an even better compromise between ride quality and anti-rollhandling stability and other characteristics.

Accordingly, the invention provides a leaf spring suspension whichcreates this better resistance to vehicle roll, such a suspension beingshown diagrammatically in FIGS. 7 to 9.

As discussed above, it is normal practice with current, prior art leafspring suspensions having an anti-roll mechanism associated therewith,to mount the torsionally rigid member 12 as close as possible to theneutral axis in bending of the leaf springs 1.

Also, those mountings are made sufficiently flexible to allow for thetransmission of torque created by the torsionally rigid member 12 but tobe considered as pin-jointed in plan view. This is achieved by makingthe brackets or other mountings for mounting the torsionally rigidmember 12 to the opposed leaf springs 1 sufficiently narrow and/orflexible, to allow the member 12 to move within its mountings.

This normal suspension practice improves assembly, reduces localstresses, creates a lightweight structure and avoids interfering withthe normal spring deflections.

The invention, however, provides a suspension which exploits the bendingstiffness of the torsionally rigid member 12 to create higher anti-rollspring stiffening, wherein the member 12 is mounted offset from theneutral axis in bending of the leaf springs and, also, is mountedrigidly thereto. This rigid mounting effectively renders the ends of thetorsionally rigid member 12 fixed, or encastre, in bending, when viewedin plan, as shown in FIG. 9.

This added rigidity creates a higher resistance force to the bending ofthe member 12 in a generally horizontal plane, which occurs when theleaf springs 1 deflect in opposite directions, during vehicle roll.

This higher-than-previous resistance force, when it acts offset from theneutral axis in bending of the leaf springs 1, creates a bending momentin the springs, which resists the change in bending which, in turn,reduces deflection of the springs 1 during vehicle roll. Thus, extrabending rigidity stiffens the springs 1 during vehicle roll and createsthis extra anti-roll function within the suspension.

This can be more readily explained when discussed in conjunction withFIGS. 7 to 10 of the drawings.

Thus, FIG. 7 is a diagrammatic side view of the suspension in accordancewith the invention, with the leaf springs 1 inverted and only theirneutral axes in bending shown, in order to simplify the discussion.

To all intents and purposes, a basic leaf spring is considered to be aregularly-sectioned beam which deflects under a bending load to create atension stress in the upper surface of the beam and a compression stressin the lower surface of the beam, the neutral axis in bending of theleaf spring being that internal layer of the beam which extendslongitudinally and approximately centrally of the section of the beam,which undergoes zero (neutral) bending stress and about which the beam(leaf spring) deflects (bends) to absorb the energy caused by suchdeflection (bending).

Thus, in FIGS. 7 and 8, the neutral axis in bending of the leaf springsis indicated at 21, when the springs are in their steady state.

Also as shown in FIGS. 7 and 8, the opposed ends of thetransversely-extending torsionally rigid member 12, shown in FIG. 9, areindicated at 22 and 23.

Also, the longitudinal axis of the torsionally rigid member 12 is offsetby a distance x from the neutral axis in bending 21 of each leaf spring1.

In accordance with the invention, the torsionally rigid member 12 hasits respective opposed ends mounted rigidly to the corresponding ends ofthe pair of leaf springs 1, so that there is no movement therebetween,however small, during use of the suspension, particularly during vehicleroll.

In FIG. 8, the upper neutral axis in bending 21′ is that of one of theleaf springs 1 in its rebound configuration, whilst the lower neutralaxis in bending 21″ is that of the other leaf spring 1 in itscompression configuration, during roll of the vehicle.

The corresponding positions of the ends 22, 23 of the torsionally rigidmember 12 are also shown in FIG. 8.

Thus, one leaf spring, on the outside of a curve or bend beingnegotiated by the vehicle, deflects further than the steady state,whilst the other spring, on the inside of the curve or bend, deflectsless than its steady state, resulting in fore and aft movement ofrespective ones of the ends 22 23 of the torsionally rigid member 12, asshown in FIG. 9.

In that Figure, the view is in plan in the direction of the arrow A inFIGS. 7 and 8, with the movements of the opposed ends 22,23 of themember 12 mounted rigidly to the leaf springs 1, being evident.

The torsionally rigid member 12 can be seen to be stressed, as if itwere a beam with fixed ends and with those ends moving apart, as if onewas a “sinking end”, as defined in applied mechanics.

This creates forces at the ends 22,23, as shown at F in both FIGS. 8 and9. These forces F act at a distance x from the neutral axes in bending21′, 21″, of the respective leaf springs 1, thus creating moments Fxaround those neutral axes in bending.

FIG. 10 is a bending moment diagram similar to that shown in FIG. 6 butwith those additional bending moments added. It can be seen that thosemoments Fx reduce further the change in bending moment during the loadchanges created by vehicle roll whilst the vehicle is manoeuvring a bendor curve.

In FIG. 10, the steady state bending moment diagram is again indicatedat 11, whilst the unrestricted compression and rebound bending momentdiagrams for the prior art suspension without an anti-roll mechanism, asshown in FIG. 1, are indicated at 12 and 13 and with an anti-rollmechanism, as shown in FIG. 5, at 14 and 15.

The improved bending moment diagrams, as reduced compression and reboundbending moment diagrams, are indicated at 31 and 32.

Thus, this lower, bending moment change generated by the inventivesuspension creates lower spring deflection, thus stiffening the springs1 and reducing roll.

Referring now to FIGS. 11 to 13 of the drawings, here is shown amounting arrangement between one end of the torsionally rigid member 12and the fore end of one of the leaf springs 1.

This mounting arrangement comprises an upper, flanged, U-shaped clamp 41and a lower, generally planar clamp 42.

The torsionally rigid member 12 which is in the form of an anti-rolltube, shown in square cross-section in FIGS. 11 to 13, is located withinthe channel defined by the upper clamp 41, as shown clearly in FIG. 13.

Between the lower clamp 42 and the flanges 43 of the upper clamp 41 andthe anti-roll tube 12, there is provided a spacer block 44 whose lowersurface is channeled at 45 to nest with the upper surface of the leafspring 1.

The arrangement is held together by a pair of U-bolts 46 which embracethe lower clamp 42 and whose upper, otherwise free ends, extend throughcorresponding holes in the flanges 43 of the upper clamp 41, withsecuring nuts 47 being provided. The lower clamping piece betterdistributes the clamping force onto the clamped leaf compared to directengagement of the U-bolts thereagainst, prevents bruising of the surfaceof the highly processed leaf during assembly and in service, andprevents associated localised corrosion. It also locates the spacing ofthe U-bolts and could be narrower to allow for a reasonable radius inthe actual U-bolt with the U-bolts tight against the sides of the leafto assist with the joint rigidity.

The neutral axis 21 in bending of the leaf spring 1 is shown in dashedlines in FIG. 13.

The mounting arrangement is clamped so tightly together by means of theU-bolts 46 and securing nuts 47 that there is no relative movementwhatsoever between the anti-roll tube 12 and leaf spring 1 within thatarrangement during use of the suspension under normal and rollconditions.

In this manner, and as discussed above, such an arrangement providesadditional stiffening for the leaf spring 1, thus reducing roll duringcornering, for example, around a bend or curve, by the associatedvehicle.

This is in distinct contrast to the prior art anti-roll suspensions,wherein the mounting arrangements for the anti-roll mechanism andassociated leaf springs are structured, to allow at least slightmovement therebetween, particularly during vehicle roll.

Additionally, the anti-roll tube 12 is offset considerably from theneutral axis 48 in bending of the leaf spring 1, which contributes tostiffening of the spring 1 during vehicle roll.

Although a spacer 44 is provided in this particular embodiment, such acomponent may be omitted, as long as the anti-roll tube is offsetsufficiently from the neutral axis 48 in bending of the leaf spring 1,to provide, in combination with the rigidly-clamped mountingarrangement, the additional stiffening of the spring 1 during vehicleroll.

Further, and in order to enhance the rigidity of the mountingarrangement, the clamping areas provided by the upper and lower clamps41,42 are comparatively large when compared against the clamping areasof prior art arrangements which, as mentioned above, are usually narrow.

Thus, in this particular embodiment of inventive leaf spring suspension,the clamping area is both comparatively wide and long to provide thegreatest possible area.

FIGS. 14 to 16 show an alternative mounting arrangement to that of FIGS.11 to 13.

The two U-bolts 46 in FIGS. 11 to 13 are replaced by four straight bolts46′ which hold the arrangement together by clamping between the upperclamp 41 and an enlarged lower clamp 42′. The lower clamp 42 of thepreceding embodiment is widened to form this larger clamp 42′ projectingoutward past both sides of the spring to provide mounting to the boltswhich now extend through both clamps 42′ and 41. The enlarged lowerclamp 42′ is strengthened over clamp 42 to enable the arrangement totransmit the bolt clamping forces onto the lower face of the spring 1 asthe replaced U bolts 46 no longer embrace the lower clamp.

FIGS. 17 to 19 show a similar mounting means to FIGS. 14 to 16 exceptthat a two-leaf assembly 1′ replaces the single-leaf leaf spring 1. Thespacer block 44 in the previous figures is extended to make a modifiedspacer 44′, which now fully embraces the spring assembly and supportsthe lower clamp 42′.

In a spring assembly using more than one leaf, the leaves have to beable to move in a sliding shearing movement relative to each other alongtheir lengthwise directions to deflect normally under a load change.This movement between the leaves needs to be in the horizontal directionof the two dimensional view shown in FIG. 19.

To create the absolute rigidity in this clamping means the upper leaf 54in FIG. 19 is clamped between lower first leaf 56 and the top portion ofthe spacer 44′ lying over the upper leaf using two elastomericinterleaves 58 and 60, one 58 provided between the two leaves and theother 60 between the upper leaf 54 and the spacer's top portion lyingthereover. These interleaves are highly compressed until they areeffectively fully bulked out with nowhere to flow further under furthercompression loads. This creates the absolute rigidity of the end of theanti-roll member relative the spring, but will allow the leaves to moveinternally relative to each other only in the required shearing actionduring normal spring deflection.

In this embodiment, the spacer that provides substantial offset of theanti-roll member 12 from the neutral axis 21 of each leaf of the springalso fully embraces around the top and sides of the spring leaves toprovide surfaces against which the top and bottom clamp pieces pressunder tightening of the bolt, because where the central span of theoriginal spacer pressed on the top face of the spring at a fixedposition therealong in the single-leaf embodiment, this area between thetop face of the top leaf and the central span of the spacer is now asliding interface at the top elastomeric interleaf in the multi-leafembodiment. Cylindrical spacers concentrically disposed around the boltscould alternatively be used in place of the full-height sides of theillustrated spacer.

The highly compressed condition of the interleaves prevents a gap fromopening between the bottom leaf and the lower clamping piece underfurther compressive loads experienced during use of the suspension, asthe maximally compressed interleaves cannot be compressed any furtherunder such loads, and so the absolute rigidity of the clamped connectionbetween the spring and the anti-roll member is maintained.

The plan view rigidity in this multi-leaf joint arrangement, to createthe fixed ended beam bending structure, is achieved in thiselastomerically interleaved structure by the frictional engagement ofthe lower leaf's lower face onto the lower clamping piece and the spacerthat now fully envelopes both leaves and the interleaves in a tight fitagainst the sides of these leaves. The interleaf compression achieves acompression force, and compression force longitudinal distribution, ontothe lower leaf to create the equivalent friction distribution to say thetwo U bolts, or 4 plain bolts, tension force. The side contact of thespacer against the leaves creates joint rigidity on both leaves, and atthe same time is accurately specified to allow the shearing upper leafmovement without too much friction.

An additional feature in the illustrated multi-leaf arrangement is thatthe lower leaf 56 is located relative to the spacer 42′ using a dowel62. This location positions the assembly accurately onto the springassemblies during production assembly. This location technique can beused in other clamping arrangements and can instead use a stud or a maleto female dimple formed on spring and spacer. Besides assisting with thecorrect assembly position, these location features also prevent thelower leaf from sliding inside the clamping on any deterioration thatthe interleaves may experience over prolonged time in service.

Although there is movement between the spring leaves along their lengthsunder deflection, the torsionally rigid anti-roll member is stillrigidly fixed to the overall spring, because although the top leaf isslidable relative to the bottom leaf, the clamping pieces don't moverelative to the bottom leaf due to the tight clamping provided by thenuts, which is aided in the illustrated embodiment by the leaf locationdowel used to initially position the components on the spring.Accordingly, using the lower leaf of the illustrated multi-leafembodiment to define the position of the overall spring, the anti-rolldevice is rigidly fixed to the spring as no relative movement is allowedto occur between the clamped end of the anti-roll device and the lowerleaf defining the spring's position, even though there is movementbetween the leaves of the spring. Accordingly, a suspension having ananti-roll device with opposite ends fixed so rigidly to opposing leafsprings of a vehicle to give the anti-roll device fixed-ended beamcharacteristics in plan view can be achieved by fixing each end to oneleaf of the respective spring rigidly enough to prevent any and allmovement of the end relative to that leaf in use of the suspension. Themain clamping rigidity for the “fixed ended beam in plan” is obtainedfrom the one leaf, but with back up from the tight side location of thespacer against all the leaves. Also, the highly clamped interleavesallow both the prior art bending resistance torque, and the new (Fx)torque, to be fully transmitted into all the leaves.

Multi-leaf embodiments in which each spring has more than two leaves maysimilarly be produced with the mounting arrangement for the end of theanti-roll device rigidly fixed to one of the leaves, an additionalinterleave member being added for each additional leaf introduced in thestack of leaves and interleaves. It will also be appreciated that theterms upper, lower, top and bottom are used in association with theillustrated orientation of the spring, anti-roll device and clampingarrangement, and that these terms are not intended to limit the mannerin which the clamping arrangement may be installed. For example, the topleaf illustrated in FIGS. 17 to 19 may actually be the lower leaf whenthe suspension system is installed on a vehicle, the shaped clampingpiece embracing the anti-roll member across the spring thickness fromthe opposing flat clamping piece thus being disposed below the springinstead of the illustrated position above the spring.

FIGS. 20 and 21 show another alternative rigid clamping arrangementmeans. In this arrangement two support members 64 and 66 are rigidlyfastened to the torsionally rigid cross tube 12′.

These support members are shown here as two plates, but they can bereplaced by other arrangements of brackets or plates. They are shownfastened to the torsionally rigid cross tube 12′ using welding. Again,any structurally rigid form of fastening could be used.

The spring assembly is clamped between two clamping plates 68 and 70using bolts 72 which pass through the spring leaf 1. While shown in thisembodiment as straight bolts passing through two clamping pieces, onecould instead use one or more U bolts each passing through only oneclamping piece and having its closed end passing around the springassembly across the spring from the clamping piece through which itpasses and is secured to by nuts, in which case a second clamping pieceagain may be positioned between the closed end of the U-bolt and thespring as opposed to direct engagement of the U-bolt against the spring.

The support plates 64 and 66 fastened to the cross tube are fastened tothe two clamping plates 68 and 70 using bolts 74 which pass throughaligned holes in the support plates and clamping plates to extend fullyover the spring in the widthwise direction thereof and clamp the wholearrangement absolutely rigid.

The different embodiments described and illustrated herein demonstratehow different mounting arrangements may be employed to clamp so tightlytogether that there is no relative movement whatsoever between theanti-roll tube 12 and leaf spring 1 within those arrangements during useof the suspension under normal and roll conditions, to considerablyoffset the anti-roll tube 12 from the neutral axis in bending of theleaf spring 1 and to provide wide and long clamping areas that arerelatively large in comparison to the prior art.

The embodiment of FIGS. 20 and 21 illustrates that the significantoffset used to provide, in combination with the rigidly-clamped mountingarrangement, the additional stiffening of the spring 1 during vehicleroll can be employed without necessarily using a spacer disposed betweenthe side edges of the spring to engage against the width-definingsurface thereof facing the anti-roll member.

All the suspensions discussed above in both the prior art and inventivearrangements show the additional member 12 at one end of the springs.This arrangement can also be applied to both ends of the springs, ifrequired.

Since various modifications can be made in my invention as herein abovedescribed, and many apparently widely different embodiments of same madewithin the spirit and scope of the claims without department from suchspirit and scope, it is intended that all matter contained in theaccompanying specification shall be interpreted as illustrative only andnot in a limiting sense.

1. A method of increasing spring stiffness during vehicle roll, in whichleaf springs extending longitudinally of a vehicle chassis on opposedsides thereof deflect in different directions, the method comprisingmounting opposed ends of an anti-roll device that extends transverselyto the vehicle chassis to respective ones of the leaf springs so rigidlyas to prevent any and all relative movement of the opposed ends of theanti-roll device to the respective ones of the leaf spring to make theanti-roll device into a fixed ended characteristic beam in plan viewsuch that when the springs deflect in different directions to eachother, as in vehicle roll, the springs change from pin-jointed beamstowards fixed ended characteristic beams, thus substantially increasingthe stiffness of the springs: wherein the step of mounting the opposedends of the anti-roll device to the respective ones of the leaf springscomprises using spacers to mount the opposed ends of the anti-rolldevice at a substantial offset distance from a neutral axis in bendingof the spring such that when the springs deflect in opposite directions,as in vehicle roll, resistant forces combine with the offset distancefrom the neutral axis to create moments in the springs to further changespring bending characteristics from pin-jointed to fixed ended beamcharacteristics, thus further substantially increasing the stiffness ofthe springs.
 2. A method of increasing spring stiffness during vehicleroll, in which leaf springs that extend longitudinally of a chassis of avehicle on opposed sides thereof deflect in different directions, themethod comprising: (a) mounting opposed ends of an anti-roll device thatextends transversely to the vehicle chassis to respective ones of theleaf springs, including (i) mounting the opposed ends of the anti-rolldevice to the respective ones of the leaf springs so rigidly as toprevent any and all relative movement of the opposed ends of theanti-roll device to the respective ones of the leaf spring to make theanti-roll device into a fixed ended characteristic beam in plan view,and (ii) using spacers to mount the opposed ends of the anti-roll deviceat a substantial offset distance from a neutral axis in bending of thesprings; and (b) when the springs deflect in different directions toeach other, as in vehicle roll, (i) changing the springs frompin-jointed beams towards fixed ended characteristic beams, thussubstantially increasing the stiffness of the springs, and (ii)combining resistant forces with the offset distance from the neutralaxis to create moments in the springs to further change spring bendingcharacteristics from pin-jointed to fixed ended beam characteristics,thus further substantially increasing the stiffness of the springs.
 3. Amethod of increasing spring stiffness during vehicle roll, in which leafsprings extending longitudinally of a vehicle chassis on opposed sidesthereof deflect in different directions, in use of a vehicle havingopposed ends of an anti-roll device that extends transversely to thevehicle chassis mounted to respective ones of the leaf springs at asubstantial offset distance from a neutral axis in bending of thesprings so rigidly as to prevent any and all relative movement of theopposed ends of the anti-roll device to the respective ones of the leafspring to make the anti-roll device into a fixed ended characteristicbeam in plan view, the method comprising, when the springs deflect indifferent directions to each other, as in vehicle roll, (i) changing thesprings from pin-jointed beams towards fixed ended characteristic beams,thus substantially increasing the stiffness of the springs, and (ii)combining resistant forces with the offset distance from the neutralaxis to create moments in the springs to further change spring bendingcharacteristics from pin-jointed to fixed ended beam characteristics,thus further substantially increasing the stiffness of the springs. 4.The method of claim 3 comprising using spacers disposed between thesprings and the anti-roll device to provide the substantial offsetdistance from the neutral axis in bending of the springs.